Performing well (2,4)
I believe the answer is:
on song
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">performing well</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for on song that I've seen before include "In superlative form" , "Performing well - in form (slang)" , "on top form?" , "Vocally" , "Performing well (colloq.)" .)